Xen users - Oct 2011 - Blank screen problem after the start of XDM with the hypervisor running

Hello,

it is more than one month I am facing with a very strange problem on
my Desktop PC.
I have the kernel 3.1.0-gentoo and I know the framebuffer doesn''t work
(I''m using a nVidia
card with nvidia-drivers) with the hypervisor.
Anyway, it''s not about a framebuffer issue I am discussing now.
I use the same kernel to start the machine in two way:

1) as a XEN hypervisor (dom0)
2) as usual (no xen hypervisor)

The Grub entries I use to select between 1 and 2 are the following:
(1) title=Gentoo Linux 3.1.0-gentoo XEN
    root (hd0,0)
    kernel /xen.gz
    module /kernel-3.1.0-gentoo root=/dev/md1
video=uvesafb:1280x1024-32,mtrr:3,ywrap

(2) title=Gentoo Linux 3.1.0-gentoo XEN
    root (hd0,0)
    kernel /kernel-3.1.0-gentoo root=/dev/md1
video=uvesafb:1280x1024-32,mtrr:3,ywrap

If I boot (2) the machine starts without the xen hypervisor and the
framebuffer is enabled.
If I boot (1) the machine also starts and with the xen hypervisor but
this time it has a problem:
once XDM has started, if I press CTRL+ALT+1 I see a blank screen (the
monitor detects
as no video input). This doesn''t happen with (2). It is not a Grub
configuration issue
(the "uvesafb" option) but I cannot see anything. I also tried to cut
that option and nothing
changed. Of course also the other console (F2->F6) aren''t available
as well.

The problem described above happens in (1) with or without the uvesafb
kernel module compiled.
It doesn''t happen in (2) with or without the uvesafb kernel module
compiled.

To make a test, I''ve tried to enable XEN also on my laptop and
I''ve
seen that this doesn''t
happen. I have a nVidia card also on the laptop and I use
nvidia-drivers even there.
Finally I''ve disabled the XEN support in the laptop kernel after this
test.

Kernel configurations:
Desktop kernel configuration: http://pastebin.com/7amx6E3L
Laptop kernel configuration: http://pastebin.com/4w23yU0n

dmesg: http://pastebin.com/5ZWsc370

Could somebody help me to understand what it is happening please?

-- 
Flavio

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